Researchers have uncovered a potential role of the bacteria found within breast tissue in the prevention and progression of breast cancer. Researchers at the Western University and the Lawson Health Research Institute in London, Ontario, Canada, found that healthy breast tissue had a higher abundance of beneficial bacteria, while women with breast cancer had a higher relative abundance of Bacillus, Enterobacteriaceae, and Staphylococcus. The study was published in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.

The study suggests that different types of bacteria can exist within breast tissue, and certain bacteria linked to a higher level of DNA damage in vitro could be detected among the samples from breast cancer patients compared with those from healthy individuals. Samples from women with breast cancer also had lower levels of lactic acid bacteria compared with healthy samples. Lactic acid bacteria have been shown to have beneficial health effects, including anticarcinogenic activity.

These results, according to Gregor Reid, PhD, and colleagues, show that the mammary tissue microbiome may be a factor in modifying risk of breast cancer development.

The researchers analyzed the breast microbiota and microbiota of adjacent healthy tissue from 45 women who had undergone surgery for breast cancer. They compared these samples with samples of breast tissue from 13 women with benign breast tumors and 23 women with no evidence of cancer who had undergone breast reductions or enhancement surgery. The team used DNA sequencing to identify the spectrum of bacterial species in each tissue sample, and culture techniques to confirm that the organisms were alive within the tissue.

The women with breast cancer had higher levels of bacteria known to induce DNA damage in the form of double-stranded breaks in cultured human cells, while bacteria associated with health-promoting benefits—Lactococccus and Streptococcus—were more abundant among those samples from healthy women.

One potential caveat to the work is the discrepancy between the ages of the diseased and healthy cohorts. The mean age of those with cancer was 62 years, while the mean age in the healthy cohort was 49 years, and 38 years in the benign tumor group. According to the authors, age is not likely to play a major role in the study because the differences in bacteria in the benign tumor and healthy cohorts were not significant.

“The knowledge that the risk of breast cancer is reduced with breastfeeding made me wonder why this might be so, especially given the beneficial microbes present in [human] milk,” Reid told Cancer Network. “Our discovery of bacteria in every region we looked at was fascinating, and the fact that there were different ones in women with cancer makes us ask, what might they be doing there?”

The work, according to Reid, “opens the door for testing if probiotic use can alter the breast microbiome and future risk of cancer.”